In many applications, it is desirable to provide strong adherent metal layers on a polymer substrate. Examples of such uses are widely diversified. For example, adherent metal coatings on polymer substrates can be used in the manufacture of printed circuit boards or as a radio interference barrier. Such coatings also have applications in the manufacture of certain types of credit cards, video disks and for decorative coatings.
Various methods have been employed for providing metal coatings on polymer surfaces. Such methods include lamination by means of an adhesive, electroless plating, and vacuum metallization. The latter method includes vacuum evaporation, sputter deposition and ion plating. While vacuum metallization has become a desirable and cost efficient method of applying metallic coatings onto polymer substrates, the adhesion of such films to the substrates is often less than adequate, especially when metallizing durable high performance polymers such as epoxy resins. The adhesion problem often becomes particularly critical where the vacuum metallized layer is further processed by electroless metal plating or electroplating to increase the thickness of the metallized layer. In such cases, the adhesion of the vacuum metallized film must withstand the environment and temperatures of subsequently employed plating baths.
Shanefield and Verdi have recently discovered a novel method for vacuum depositing an adherent metal layer or film on a particular type of epoxy substrate. Unfortunately, when the substrate bearing the film was subsequently treated in electroless plating baths as are commonly used in the manufacture of printed circuit boards, blistering and delamination often occurred during the electroless plating. We have now discovered a modification of the Shanefield and Verdi process which prevents the blistering or delamination of the vacuum deposited films when subjected to electroless plating baths.